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Annie,I was interested (and troubled) by your statement that 'data from 1751 to 1994 showed a decrease from approximately 8.179 to 8.104'. Could you please provide a source for these data?

My understanding is that the 1750-1994 figure is an estimate, back-cast by modelling the estimated carbon dioxide emissions (themselves estimated from estimated fossil fuel combustion over the period). If there were sufficient data on ocean pH in 1750 to derive a global estimate, I would be very keen to hear of them. I further understand that this change lies within the range of the current observed regional variation of oceanic pH, and that the data from 1994 come from very limited sources and we had nothing near global data until quite recently.

Please provide the evidence that I am wrong.

Coincidentally, Matt Ridley has posted in the past couple of days on the issue. He provides citations to a considerable number of recent papers that point to the problem being overstated. In particular, not only does observational science suggest less harm to biota which (surprisingly) are capable of adaptation, but there is even evidence of positive effects. One problem with the apocalyptic acidification meme appears to be that it focuses on carbonate rather than bicarbonate (the AAD, including its 'Fact Sheet' appears to make this error), and bicarbonate availability seems to increase with declining pH (I say decreasing alkalinity, you say increasing acidity - 'let's call the whole thing off!') (See: http://www.rationaloptimist.com/blog/acid-oceans-and-acid-rain)